Visualization of Sulfur Chemical State of Cathode Active Materials for Lithium–Sulfur Batteries by Tender X‑ray Spectroscopic Ptychography

Lithium–Sulfur batteries are rechargeable batteries that have attracted much attention in recent years because of their large theoretical capacity and the low cost of sulfur. However, there is an obstacle to the development of cathode materials for practical use: the reaction and degradation mechanisms during the charge–discharge process are not fully understood. In this study, we demonstrated the visualization of the sulfur chemical state of cathode active materials at a high spatial resolution using tender X-ray spectroscopic ptychography. We measured the sulfurized poly­(n-butyl methacrylate) (SPBMA) samples in the form of particles and small pieces of cathode composites at the S K-edge (∼2.47 keV) and successfully visualized the heterogeneous distribution of sulfur chemical state parameters and their trend changes by the charge/discharge processes in them. We found that the distribution of sulfur chemical states in SPBMA particles is heterogeneous and that traces of the discharge reaction exist near the particle surface. We also found that the cathode composites accumulated sulfur oxides, possibly due to side reactions between sulfur and the electrolyte.